When you add a domain as hosted in some account, you usually set a pair of Name Servers to direct it to that particular service provider. On their end, three records are set up automatically the moment the domain address is added - one A record and two MX records. The first one is a numeric address, or IP address, that “tells” the Internet domain where its website is, while the other two are alphanumeric and they reveal the server that handles the e-mails for that specific Internet domain. The site and the e-mail hosting are often thought to be one thing, when they're in fact two different services. Having separate records for them will allow you to have them with different providers if you want. As an illustration, some new service provider may have outstanding uptime for your site, but you might not want to switch your e-mail messages from your current host and by using an A record to point the domain name to the first and MX records to have the emails with the second, you will get the best of both companies. These records are checked when you want to open a site or send an e-mail - either way, the company whose name servers are used for the Internet domain is going to be contacted to retrieve the A and MX records and if you've set records different from their own, the correct web/mail server will then be contacted and you are going to see the needed website or your email is going to be delivered.